Evaluation of liposome toll-like receptor ligand complexes for non-specific mucosal immunoprotection from feline herpesvirus-1 infection

Comparison of Antiviral Immune Responses in Healthy Cats Induced by Two Immune Therapeutics

BACKGROUND

Effective immunotherapeutic agents for use in cats are needed to aid in the management of intractable viral diseases, including feline infectious peritonitis (FIP) infection. The objectives of this study were to compare two different immune stimulants for antiviral activity in cats: (1) TLR 2/6-activating compound polyprenyl immunostimulant; (PI) and (2) liposome Toll-like receptor 3/9 agonist complexes (LTCs) to determine relative abilities to stimulate the induction of type I (IFN-α, IFN-β) and type II (IFN-γ) interferon immune responses in vitro and to study the effects of treatment on immune responses in healthy cats.

METHODS

Cytokine and cellular immune responses to PI and LTC were evaluated using peripheral blood mononuclear cells (PBMCs) from healthy cats incubated with LTC and PI at indicated concentrations using reverse transcriptase polymerase chain reaction assays and ELISA assays. The effects of the immune stimulants on inhibiting FIPV replication were assessed using a feline macrophage cell line (fcwf-4). Cytokine and cellular immune responses to PI and LTC were evaluated in blood samples from healthy cats treated with PI and LTC, using reverse transcriptase polymerase chain reaction (RT-PCR) and ELISA assays.

RESULTS

In the in vitro studies, both compounds triggered the upregulated expression of IFN-α, IFN-γ, and IL-1β genes in cat PBMC, whereas treatment with LTC induced significantly greater expression of IFN-α and IFN-γ on Day 1 and IL-1b on Day 3. There was significant protection from FIPV-induced cytopathic effects when fcwf-4 cells were treated with conditioned medium from LTC-activated leukocytes. In the healthy cat study (in vivo), both PI and LTC increased the mRNA signal for IFN-α, IFN-γ, and IL-1β above baseline at multiple time points with statistically greater increases in the LTC group on either Day 1 (IFN-α, IFN-γ) or Day 3 (IL-1β). In addition, RANTES increased over time in cats treated with the LTC.

CONCLUSIONS

Both LTC and PI protocols induced immune-enhancing effects, suggesting a possible clinical use for the management of chronic infectious diseases like FIP. Activating the TLR 3 and 9 pathways (LTC) induced superior broad interferon production in vitro than the activation of the TLR 2 and 6 pathways (PI).

Evaluation of Immune Nanoparticles for Rapid and Non-Specific Activation of Antiviral and Antibacterial Immune Responses in Cattle, Swine, and Poultry

Given the rapid potential spread of agricultural pathogens, and the lack of vaccines for many, there is an important unmet need for strategies to induce rapid and non-specific immunity against these viral and bacterial threats. One approach to the problem is to generate non-specific immune responses at mucosal surfaces to rapidly protect from entry and replication of both viral and bacterial pathogens. Using complexes of charged nanoparticle liposomes with both antiviral and antibacterial toll-like receptor (TLR) nucleic acid ligands (termed liposome-TLR complexes or LTC), we have previously demonstrated considerable induction of innate immune responses in nasal and oropharyngeal tissues and protection from viral and bacterial pathogens in mixed challenge studies in rodents, cattle, and companion animals. Therefore, in the present study, we used in vitro assays to evaluate the ability of the LTC immune stimulant to activate key innate immune pathways, particularly interferon pathways, in cattle, swine, and poultry. We found that LTC complexes induced strong production of type I interferons (IFNα and IFNβ) in both macrophages and leukocyte cultures from all three species. In addition, the LTC complexes induced the production of additional key protective cytokines (IL-6, IFNγ, and TNFα) in macrophages and leukocytes in cattle and poultry. These findings indicate that the LTC mucosal immunotherapeutic has the capability to activate key innate immune defenses in three major agricultural species and potentially induce broad protective immunity against both viral and bacterial pathogens. Additional animal challenge studies are warranted to evaluate the protective potential of LTC immunotherapy in cattle, swine, and poultry.

Nanoparticle ocular immunotherapy for herpesvirus surface eye infections evaluated in cat infection model

Ocular herpes simplex type 1 (HSV-1) infections can trigger conjunctivitis, keratitis, uveitis, and occasionally retinitis, and is a major cause of blindness worldwide. The infections are lifelong and can often recrudesce during periods of stress or immune suppression. Currently HSV-1 infections of the eye are managed primarily with anti-viral eye drops, which require frequent administration, can cause irritation, and may take weeks for full resolution of symptoms. We therefore evaluated the effectiveness of an ocular immune activating nanoparticle eye drop as a novel approach to treating HSV-1 infection, using a cat feline herpesvirus -1 (FHV-1) ocular infection model. In vitro studies demonstrated significant induction of both type I and II interferon responses by the liposome-dual TLR 3/9 agonist nanoparticles, along with suppression of FHV-1 replication. In cats with naturally occurring eye infections either proven or suspected to involve FHV-1, ocular nanoparticle treated animals experienced resolution of signs within several days of treatment, including resolution of keratitis and corneal ulcers. In a cat model of recrudescent FHV-1 infection, cats treated twice daily with immune nanoparticle eye drops experienced significant lessening of ocular signs of infection and significantly fewer episodes of viral shedding compared to control cats. Treatment was well-tolerated by all cats, without signs of drug-induced ocular irritation. We concluded therefore that non-specific ocular immunotherapy offers significant promise as a novel approach to treatment of HSV-1 and FHV-1 ocular infections.

Nanocarriers for effective delivery: modulation of innate immunity for the management of infections and the associated complications

Innate immunity is the first line of defense against invading pathogens. Innate immune cells can recognize invading pathogens through recognizing pathogen-associated molecular patterns (PAMPs) via pattern recognition receptors (PRRs). The recognition of PAMPs by PRRs triggers immune defense mechanisms and the secretion of pro-inflammatory cytokines such as TNF-α, IL-1β, and IL-6. However, sustained and overwhelming activation of immune system may disrupt immune homeostasis and contribute to inflammatory disorders. Immunomodulators targeting PRRs may be beneficial to treat infectious diseases and their associated complications. However, therapeutic performances of immunomodulators can be negatively affected by (1) high immune-mediated toxicity, (2) poor solubility and (3) bioactivity loss after long circulation. Recently, nanocarriers have emerged as a very promising tool to overcome these obstacles owning to their unique properties such as sustained circulation, desired bio-distribution, and preferred pharmacokinetic and pharmacodynamic profiles. In this review, we aim to provide an up-to-date overview on the strategies and applications of nanocarrier-assisted innate immune modulation for the management of infections and their associated complications. We first summarize examples of important innate immune modulators. The types of nanomaterials available for drug delivery, as well as their applications for the delivery of immunomodulatory drugs and vaccine adjuvants are also discussed.

Feline Coronavirus and Alpha-Herpesvirus Infections: Innate Immune Response and Immune Escape Mechanisms

Over time, feline viruses have acquired elaborateopportunistic properties, making their infections particularly difficult to prevent and treat. Feline coronavirus (FCoV) and feline herpesvirus-1 (FeHV-1), due to the involvement of host genetic factors and immune mechanisms in the development of the disease and more severe forms, are important examples of immune evasion of the host's innate immune response by feline viruses.It is widely accepted that the innate immune system, which providesan initial universal form of the mammalian host protection from infectious diseases without pre-exposure, plays an essential role in determining the outcome of viral infection.The main components of this immune systembranchare represented by the internal sensors of the host cells that are able to perceive the presence of viral component, including nucleic acids, to start and trigger the production of first type interferon and to activate the cytotoxicity by Natural Killercells, often exploited by viruses for immune evasion.In this brief review, we providea general overview of the principal tools of innate immunity, focusing on the immunologic escape implemented byFCoVand FeHV-1 duringinfection.

Non-specific protection from respiratory tract infections in cattle generated by intranasal administration of an innate immune stimulant

Alternatives to antibiotics for prevention of respiratory tract infections in cattle are urgently needed given the increasing public and regulatory pressure to reduce overall antibiotic usage. Activation of local innate immune defenses in the upper respiratory tract is one strategy to induce non-specific protection against infection with the diverse array of viral and bacterial pathogens associated with bovine respiratory disease complex (BRDC), while avoiding the use of antibiotics. Our prior studies in rodent models demonstrated that intranasal administration of liposome-TLR complexes (LTC) as a non-specific immune stimulant generated high levels of protection against lethal bacterial and viral pathogens. Therefore, we conducted studies to assess LTC induction of local immune responses and protective immunity to BRDC in cattle. In vitro, LTC were shown to activate peripheral blood mononuclear cells in cattle, which was associated with secretion of INFγ and IL-6. Macrophage activation with LTC triggered intracellular killing of Mannheimia hemolytica and several other bacterial pathogens. In studies in cattle, intranasal administration of LTC demonstrated dose-dependent activation of local innate immune responses in the nasopharynx, including recruitment of monocytes and prolonged upregulation (at least 2 weeks) of innate immune cytokine gene expression by nasopharyngeal mucosal cells. In a BRDC challenge study, intranasal administration of LTC prior to pathogen exposure resulted in significant reduction in both clinical signs of infection and disease-associated euthanasia rates. These findings indicate that intranasal administration of a non-specific innate immune stimulant can be an effective method of rapidly generating generalized protection from mixed viral and bacterial respiratory tract infections in cattle.

Advances and challenges in nanocarriers and nanomedicines for veterinary application

To ensure success in the development and manufacturing of nanomedicines requires forces of an interdisciplinary team that combines medicine, engineering, chemistry, biology, material and pharmaceutical areas. Numerous researches in nanotechnology applied to human health are available in the literature. Althought, the lack of nanotechnology-based pharmaceuticals products for use exclusively in veterinary pharmacotherapy creates a potential area for the development of innovative products, as these animal health studies are still scarce when compared to studies in human pharmacotherapy. Nano-dosage forms can ensure safer and more effective pharmacotherapy for animals and can more be safer for the consumers of livestock products, once they can offer higher selectivity and smaller toxicity associated with lower doses of the drugs. In addition, the development and production of nanomedicines may consolidate the presence of pharmaceutical laboratories in the global market and can generate greater profit in a competitive business environment. To contribute to this scenario, this article provides a review of the main nanocarriers used in nanomedicines for veterinary use, with emphasis on liposomes, nanoemulsions, micelles, lipid nanoparticles, polymeric nanoparticles, mesoporous silica nanoparticles, metallic nanoparticles and dendrimers, and the state of the art of application of these nanocarriers in drug delivery systems to animal use. Finnaly, the major challenges involved in research, scale-up studies, large-scale manufacture, analytical methods for quality assessment, and regulatory aspects of nanomedicines were discussed.

Local immune and microbiological responses to mucosal administration of a Liposome-TLR agonist immunotherapeutic in dogs

Background

Non-specific immunotherapeutics have been evaluated previously in dogs, primarily for cancer treatment. However, there remains a need for a more broadly targeted, general purpose immunotherapeutic capable of activating innate immune defenses for non-specific protection or early treatment of viral and bacterial infections. To address need, our group has developed a liposomal immune stimulant (liposome-TLR complexes, LTC) containing TLR 3 and 9 agonists specifically designed to activate mucosal immune defenses in sites such as nasal cavity and oropharynx, following topical delivery. In this study, we evaluated the local immune stimulatory properties of LTC in vitro and in healthy purpose-bred dogs, including activation of cellular recruitment and cytokine production. The ability of LTC treatment to elicit effective antiviral immunity was assessed in dogs following a canine herpesvirus outbreak, and the impact of LTC treatment on the local microbiome of the oropharynx was also investigated.

Results

These studies revealed that LTC potently activated innate immune responses in vitro and triggered significant recruitment of inflammatory monocytes and T cells into the nasal cavity and oropharynx of healthy dogs. Administration of LTC to dogs shortly after an outbreak of canine herpesvirus infection resulted in significant reduction in clinical signs of infection. Interestingly, administration of LTC to healthy dogs did not disrupt the microbiome in the oropharynx, suggesting resiliency of the microflora to transient immune activation.

Conclusions

Taken together, these results indicate that LTC administration mucosally to dogs can trigger local innate immune activation and activation of antiviral immunity, without significantly disrupting the composition of the local microbiome. Thus, the LTC immune stimulant has potential for use as a non-specific immunotherapy for prevention or early treatment of viral and bacterial infections in dogs.

Evaluation of liposome toll-like receptor ligand complexes for non-specific mucosal immunoprotection from feline herpesvirus-1 infection

Background

Feline herpesvirus‐1 (FHV‐1) infection can result in serious morbidity and mortality, especially in kittens. Immunotherapy using liposome‐toll‐like receptor (TLR) ligand complexes (LTC) has been shown to activate innate immune responses.

Objectives

To determine in kittens whether mucosal administration of LTC before FHV‐1 inoculation would decrease severity of clinical signs and decrease quantities of FHV‐1 DNA in materials collected on oropharyngeal swabs.

Animals

Nineteen, 14‐week‐old, purpose‐bred kittens.

Methods

Pilot clinical trial with 2 groups of kittens allocated to either an LTC or control group. The LTC were administered into both nares and the oropharynx of the 12 LTC group kittens, and all 19 kittens were inoculated with FHV‐1 24 hours later. Clinical scores were determined daily for 28 days, and oropharyngeal mucosal materials were collected every 7 days to assess FHV‐1 DNA quantities for comparison between groups.

Results

Conjunctivitis was more common in kittens in the control group on Days 15‐28 (P = .01) and Days 1‐28 (P = .02). Total respiratory scores were higher in the LTC group on days 15‐28 (P = .03). The LTC group had significantly decreased FHV‐1 DNA on swabs when compared to the control group on some postinoculation days, using 2 methods of calculation.

Conclusions and Clinical Importance

Administration of LTC to kittens was shown to decrease FHV‐1 DNA and some manifestations of illness in kittens when administrated 24 hours before inoculation, suggesting clinical benefit.

Activation of upper respiratory tract mucosal innate immune responses in cats by liposomal toll-like receptor ligand complexes delivered topically

BACKGROUND

Nonspecific induction of local innate immune responses by mucosally administered immunotherapy is a new approach to protection from upper respiratory tract infections. Therefore, a new liposome-toll-like receptor complex (LTC) immune stimulant was developed and investigated for its ability to activate innate immune responses in cats, both in vitro and in vivo, as part of an initial evaluation of LTC for use as an immunotherapeutic agent in cats.

OBJECTIVES

We hypothesized that LTC could activate innate immune responses in cats after topical application to nasal and oropharyngeal mucosal surfaces.

ANIMALS

Mucosal immune responses to topical administration of LTC were assessed in 7 healthy, purpose-bred cats, and in vitro responses were assessed using blood samples from healthy cats.

METHODS

Cytokine and cellular immune responses to LTC were evaluated in blood samples, nasal lavage specimens, and pharyngeal swabs from cats, using reverse transcriptase polymerase chain reaction assays, ELISA assays, and flow cytometry.

RESULTS

Liposome-TLR complexes rapidly activated leukocytes in vitro, including upregulation of costimulatory molecule expression and cytokine production. Topical administration of LTC in healthy cats triggered rapid recruitment of monocytes to the nasal and oropharyngeal mucosa.

CONCLUSIONS AND CLINICAL IMPORTANCE

Liposome-TLR complexes were found to effectively activate innate immune responses in cats after mucosal administration. These findings suggest that LTC have potential for use as a new mucosally administered immunotherapy for nonspecific protection from viral and bacterial respiratory tract infections.